No abstract

A rapid and sensitive method for the determination of the total glucosinolate content in rapeseed is described. The method is based on the specific UV absorbance of the thioureas and oxazolidine‐2‐thiones. Results obtained were confirmed by gas‐liquid chromatography. Recoveries varying from 94 to 103% were obtained for samples containing mixtures of isothiocyanate and oxazolidine‐2‐thione (a total of 0.25 to 0.78 mg per assay). The relative stadard deviation for rapeseed meals varied from 4 to 10% for the total glucosinolate content (expressed as 3‐butenylisothiocyanate) and depended on the size of sample taken. The relative standard deviation for oxazolidine‐2‐thione varied from 5 to 35% for the same meal. The lower limit of detection for rapeseed meal is of the order of 0.25 mg of 3‐butenylisothiocyanate per g.

A method has been developed for the quantitative determination of the major individual thioglucosides (as their aglycones) in rapeseed on a micro scale. The thioglucosides in the meal were hydrolyzed with myrosinase (B.C. 3.2.3.1, thioglucoside glucohydrolase), and the released aglycones were extracted with methylene chloride. The 3‐butenyl and 4‐pentenyl isothiocyanates were determined by gas‐liquid chromatography. The 5‐vinyl‐2‐oxazolidinethione was determined on an aliquot of the same extract by ultraviolet absorption. Five to 20 milligrams of seed or meal were used, and one operator could analyze 24 samples per day. The standard deviation was ŷ3% for the isothiocyanates and ŷ6% for the oxazolidinethione. The limit of detection was 0.1 mg per gram of meal for the isothiocyanates and 0.3 mg per gram of meal for the oxazolidinethione. Small amounts of phenylethyl isothiocyanate and two unidentified isothiocyanates were also found.

affect an electrostatic repulsion dependent upon the charge density of the complexing anion. In order to conform to the observation that increasing the ionic strength of the same salt does not affect the energy of activation, we would have to postulate that these sites are fully saturated at low salt concentrations.The following scheme is the summary of the proposed mechanism of collagen formation and its reversal T -*• T* Collagen where T is tropocollagen, ', the inactive form and T*, the proposed intermediate that is being formed during the lag period. ' is formed when active sites on tropocollagen are blocked by anions, cations or by such agents as urea.Conditions which enhance hydrogen bonding favor the formation of collagen, while those which rupture hydrogen bonds reverse the equilibrium. The equilibrium rate will be influenced by pH, type and ionic strength of the salt present, concentration of the protein and temperature. Thus, when the collagen solution is removed from the presence of the fiber and conditions are adjusted to favor collagen formation, the system will remain poised unless conditions also favor a reasonable rate of reaction.In writing this paper, we have avoided the use of such terms as neutral-soluble or acid-soluble collagen. The impressions gained from this work have cast considerable doubt in our minds as to whether such differences really exist. It must be realized that when HO Ac solutions of collagen are adjusted to values above pH 7, the optimum pH of fiber formation is being approached. If the other variables are such as to favor coagulation, fiber formation will occur.If not, a collagen solution which is soluble in neutral or alkaline solutions will be obtained. We have found that after coagulation, the fibers can be redissolved in HO Ac, the collagen reneutralized, and fibril formation repeated as before.

L-Methionine-35S and DL-cysteine-35S were good sources of sulfur for the biosynthesis of sinigrin in Armoracia lapathifolia Gilib. and were incorporated with approximately the same efficiency. Homomethionine-35S was a slightly poorer source of sulfur than methionine, while taurine-35S was a very poor source. When homomethionine, methionine, and cysteine were employed as sources of sulfur, the distribution of radioactivity between the two sulfur atoms in sinigrin was approximately 80% in the isothiocyanate moiety and 10–15% in the sulfate moiety. When taurine was employed, the distribution was reversed. 1-Thio-β-D-glucose (1-thioglucose) also was a poor source of sulfur for sinigrin. The carbon skeleton of 1-thioglucose was only slightly incorporated into this thioglucoside. The experiments indicated that 1-thioglucose was not a direct precursor of the 1-thioglucosyl residue of sinigrin.The administration of doubly labeled methionine-2-14C-35S clearly demonstrated that this amino acid was not incorporated intact into sinigrin. The carbon-2 and sulfur atoms were metabolized by two different routes.Preliminary studies related to sulfur incorporation into the thioglucosides of Nasturtium officinale R.Br., Tropaeolum majus L., and Reseda luteola L. indicated that there were some differences depending on the source of sulfur; DL-cysteine was a better source of sulfur than either methionine or 1-thioglucose. Tropaeolum majus L. appeared to utilize the sulfur of cysteine for the production of thioglucoside as efficiently as Armoracia lapathifolia Gilib.; however, the other two species utilized the sulfur from the amino acids very poorly.